The present invention relates to a superconductor filter device including a superconductor filter and a manufacturing method of a superconductor filter device, and in particular, to a superconductor filter device and a manufacturing method of a superconductor filter device, by which desired transmission characteristics of the superconductor filter can be obtained without the need of a filter adjustment process by means of filter pattern processing.
Mobile radio communication devices (portable cellular phones, PHS (Personal Handy-phone System) terminals, etc.) have been showing a remarkable increase in number these days. Along with the increase, the number of mobile radio communication services or companies providing the services has also increased. Such a situation requires the frequency bandwidth for each communication link to be narrower and the frequency difference between frequency areas occupied by the services to be smaller, and a variety of measures for attaining the objects by saving the frequency resources have been proposed and studied. If the frequency difference between frequency areas of the services is made smaller, interference between adjacent frequency areas is easily caused and thereby various problems occur due to the interference. In order to resolve and eliminate the problems, a filter having both a steep (almost rectangular) attenuation property and transmission characteristics with small losses is desired and required. The superconductor filter can be regarded today as a unique filter that can satisfy the desired characteristics. However, in order to attain a desired steep attenuation property, a high precision superconductor filter has to be manufactured and a filter adjustment process has to be executed in the manufacturing process of the superconductor filter. Whether the superconductor filter shows desired transmission characteristics or not is observed and judged at a very low temperature, therefore, it is difficult to conduct filter pattern adjustment, screwing adjustment, etc. along with observing the transmission characteristics of the superconductor filter at the low temperature, differently from the case of ordinary filters.
The filter adjustment process of the superconductor filter has been executed so far by manufacturing the superconductor filter so as to have a little longer resonator pattern, cooling the superconductor filter into its superconducting state for observing the transmission characteristics, observing the transmission characteristics of the superconductor filter and checking the difference between the observed characteristics and desired characteristics, returning the superconductor filter into room temperature, processing the little longer resonator pattern of the superconductor filter by means of etching, laser beams, etc. so as to compensate the difference between the observed characteristics and desired characteristics, cooling the superconductor filter again, and observing and checking the transmission characteristics of the superconductor filter again. If the desired characteristics can not be obtained, the above filter adjustment process is repeated until the desired transmission characteristics are obtained.
The conventional manufacturing method (filter adjustment method) of a superconductor filter device which has been described above takes very long adjustment time including time for cooling the superconductor filter, time for returning the superconductor filter to room temperature, etc., and due to the accumulation of thermal stress caused by the temperature cycles, the operating life of the superconductor filter is necessitated to be shortened.
There has been proposed another manufacturing method (filter adjustment method) of a superconductor filter device in Japanese Patent Application Laid-Open No.HEI7-254734, in which the filter pattern of a superconductor filter held in its superconducting state is irradiated with a laser beam and thereby the filter pattern which has been formed a little longer is cut so as to have the desired transmission characteristics. The filter adjustment method can shorten the adjustment time and reduce the thermal stress due to the temperature cycles to minimum.
However, for executing the filter adjustment successfully, precise positioning of the filter pattern is required with respect to the irradiation point of the laser beam when the superconductor filter is installed in a vacuum chamber. If the positioning accuracy of the laser beam irradiation point is lower than a required pattern processing dimension accuracy, fine adjustment of the transmission characteristics of the superconductor filter is impossible. Further, due to the laser radiation, deterioration of the superconductive materials occurs and thereby the unloaded Q of the resonator is decreased. Consequently, transmission loss of the superconductor filter becomes larger. Furthermore, the filter adjustment by means of the laser beam is an irreversible adjustment, and thus it is impossible to regain the original transmission characteristics once the adjustment is executed excessively.
It is therefore the primary object of the present invention to provide a superconductor filter device and a manufacturing method of a superconductor filter device, by which the adjustment of the transmission characteristics of the superconductor filter can be executed easier without the need of the adjustment by means of filter pattern processing.
Another object of the present invention is to provide a superconductor filter device and a manufacturing method of a superconductor filter device, by which desired transmission characteristics can be obtained without deteriorating the properties of the superconductor filter.
In accordance with a first aspect of the present invention, there is provided a superconductor filter device comprising a superconductor filter, a hermetic filter case and gas. The superconductor filter operates as a filter in its superconducting state. The hermetic filter case stores the superconductor filter so that electrical connection can be provided between the superconductor filter and the outside of the hermetic filter case. The gas, which does not deteriorate or react with the superconductor filter, is packed in the hermetic filter case to an appropriate amount by which one or more transmission characteristics of the superconductor filter at a predetermined temperature (such as the center frequency of the superconductor) are adjusted to desired transmission characteristics.
In accordance with a second aspect of the present invention, in the first aspect, the superconductor filter device further comprises a hermetic outer case. The hermetic outer case stores the hermetic filter case and is evacuated into vacuum so that temperature control of the superconductor filter can be executed easily and correctly.
In accordance with a third aspect of the present invention, in the second aspect, the superconductor filter device further comprises pipes for implementing air/gas flow between the inside of the hermetic filter case and the outside of the hermetic outer case.
In accordance with a fourth aspect of the present invention, in the third aspect, the superconductor filter device further comprises valves for enabling/disabling the air/gas flow through the pipes.
In accordance with a fifth aspect of the present invention, in the third aspect, the pipes are provided with pipe joint means. The pipes are disconnected at the pipe joint means so that temperature control of the superconductor filter can be executed easily and correctly.
In accordance with a sixth aspect of the present invention, in the second aspect, the superconductor filter device further comprises a cooling means for cooling and controlling the temperature of the superconductor filter.
In accordance with a seventh aspect of the present invention, in the first aspect, the gas which is packed in the hermetic filter case is inert gas.
In accordance with an eighth aspect of the present invention, in the seventh aspect, the inert gas which is packed in the hermetic filter case is argon gas.
In accordance with a ninth aspect of the present invention, in the seventh aspect, the inert gas which is packed in the hermetic filter case is helium gas.
In accordance with a tenth aspect of the present invention, in the first aspect, gas whose liquefaction temperature is lower than the critical temperature of the superconductor filter is used as the gas which is packed in the hermetic filter case.
In accordance with an eleventh aspect of the present invention, in the first aspect, the superconductor filter is a microstrip line filter.
In accordance with a twelfth aspect of the present invention, in the eleventh aspect, the filter pattern of the superconductor filter is formed as a parallel-coupled-line-type microstrip line filter.
In accordance with a thirteenth aspect of the present invention, in the eleventh aspect, the filter pattern of the superconductor filter is formed as an interdigital filter.
In accordance with a fourteenth aspect of the present invention, in the eleventh aspect, the filter pattern of the superconductor filter is formed as a combline filter.
In accordance with a fifteenth aspect of the present invention, in the first aspect, the superconductor filter device is used as a highpass filter, a lowpass filter, a bandpass filter or a band elimination filter.
In accordance with a sixteenth aspect of the present invention, in the first aspect, the superconductor filter is formed of oxide superconductor materials.
In accordance with a seventeenth aspect of the present invention, in the first aspect, the electrical connection between the superconductor filter and the outside of the hermetic filter case is provided by use of hermetic RF connectors to which coaxial RF cables can be connected Ad detachably.
In accordance with an eighteenth aspect of the present invention, there is provided a manufacturing method of a superconductor filter device. The manufacturing method comprises a filter storage step and a frequency adjustment step. In the filter storage step, a superconductor filter which operates as a filter in its superconducting state is stored in a hermetic filter case so that an electrical connection can be provided between the superconductor filter and the outside of the hermetic filter case. In the frequency adjustment step, gas that does not deteriorate or react with the superconductor filter is packed in the hermetic filter case to an appropriate amount, and thereby one or more transmission characteristics of the superconductor filter at a predetermined temperature such as the center frequency are adjusted to desired transmission characteristics.
In accordance with an eighteenth aspect of the present invention, there is provided a manufacturing method of a superconductor filter device. The manufacturing method comprises a filter storage step, a case storage step, an evacuation step, a cooling step, a superconducting state judgment step, a gas packing step, a transmission characteristics adjustment step and a hermetic filter case sealing step. In the filter storage step, a superconductor filter which operates as a filter in its superconducting state is stored in a hermetic filter case so that electrical connection can be provided between the superconductor filter and the outside of the hermetic filter case. In the case storage step, the hermetic filter case storing the superconductor filter is stored in a hermetic outer case so that electrical connection can be provided between the superconductor filter and the outside of the hermetic outer case and so that air/gas flow through pipes can be implemented between the inside of the hermetic filter case and the outside of the hermetic outer case. In the evacuation step, the hermetic filter case and the hermetic outer case are evacuated into vacuum. In the cooling step, the superconductor filter is cooled below its critical temperature. In the superconducting state judgment step, it is judged whether or not the superconductor filter is showing its superconducting state. In the gas packing step, gas that does not deteriorate or react with the superconductor filter is gradually packed in the hermetic filter case and thereby the dielectric constant around the superconductor filter is raised from the dielectric constant of vacuum, after the superconducting state of the superconductor filter could be observed in the superconducting state judgment step. In the transmission characteristics adjustment step, the amount of the gas packed in the hermetic filter case is increased/decreased through the pipes while observing the change of one or more transmission characteristics of the superconductor filter due to the gas until desired transmission characteristics of the superconductor filter are obtained. In the hermetic filter case sealing step in which the increase/decrease of the gas is stopped by hermetically sealing the hermetic filter case so that the amount of the gas in the hermetic filter case will thereafter be fixed.
In accordance with a twentieth aspect of the present invention, in the nineteenth aspect, the manufacturing method of a superconductor filter device further comprises a thermal isolation step. In the thermal isolation step, the pipes for implementing the air/gas flow between the inside of the hermetic filter case and the outside of the hermetic outer case are disconnected at pipe joint sections which are provided between the hermetic filter case and the hermetic outer case and thereby the hermetic filter case is thermally isolated from outside.
In accordance with a twenty-first aspect of the present invention, in the eighteenth aspect, the gas which is packed in the hermetic filter case is inert gas.
In accordance with a twenty-second aspect of the present invention, in the twenty-first aspect, the inert gas which is packed in the hermetic filter case is argon gas.
In accordance with a twenty-third aspect of the present invention, in the twenty-first aspect, the inert gas which is packed in the hermetic filter case is helium gas.
In accordance with a twenty-fourth aspect of the present invention, in the eighteenth aspect, gas whose liquefaction temperature is lower than the critical temperature of the superconductor filter is used as the gas which is packed in the hermetic filter case.
In accordance with a twenty-fifth aspect of the present invention, in the eighteenth aspect, the superconductor filter is a microstrip line filter.
In accordance with a twenty-sixth aspect of the present invention, in the twenty-fifth aspect, the filter pattern of the superconductor filter is formed as a parallel-coupled-line-type microstrip line filter.
In accordance with a twenty-seventh aspect of the present invention, in the twenty-fifth aspect, the filter pattern of the superconductor filter is formed as an interdigital filter.
In accordance with a twenty-eighth aspect of the present invention, in the twenty-fifth aspect, the filter pattern of the superconductor filter is formed as a combline filter.
In accordance with a twenty-ninth aspect of the present invention, in the eighteenth aspect, the superconductor filter is formed as a highpass filter, a lowpass filter, a bandpass filter or a band elimination filter.
In accordance with a thirtieth aspect of the present invention, in the eighteenth aspect, the superconductor filter is formed of oxide superconductor materials.
In accordance with a thirty-first aspect of the present invention, in the eighteenth aspect, the electrical connection between the superconductor filter and the outside of the hermetic filter case is provided by use of hermetic RF connectors to which coaxial RF cables can be connected detachably.